1. Field of the Invention
The present invention relates to a method for selecting a material which is preferably usable to construct an ink flow passage of an ink-jet recording apparatus so that the high reliability and the high image quality are stably obtained not only when the material is in the initial state in which the ink flow passage of the ink-jet recording apparatus is filled with the ink but also when the material undergoes the temperature change and/or the time-dependent change.
2. Description of the Related Art
Those known as the ink-jet recording system include, for example, the bubble system in which the ink is discharged from minute nozzles by the aid of bubbles generated by the sudden heating, and the piezoelectric system in which the ink is discharged from minute nozzles by using the piezoelectric element which is deformed in accordance with the voltage application. In this printing technique, the inks of several colors as basic colors are converted into minute liquid droplets of several picoliters to several tens picoliters which are selectively landed on the paper surface so that an image is formed thereby. In recent years, it has been investigated to miniaturize the ink-jet recording apparatus. For example, U.S. 2003/0107625 A1 (Japanese Patent Application Laid-open No. 2003-175631) discloses an apparatus in which an ink-retaining section for retaining the ink is provided separately from a head, and the ink is supplied from the ink-retaining section through a tube to the head.
The ink-jet recording system is advantageous in the high printing quality of letters and the high printing quality of images owing to the discharge control of the minute liquid droplets, wherein the minute liquid droplets of several picoliters are landed onto the paper surface highly accurately, and thus it is possible to form the image which has no granular texture and which possesses the color reproduction approximate to the full color. In order to make it possible to discharge the minute liquid droplets as described above, it is necessary to adopt a technique for highly accurately control the landing from the sufficiently thin discharge nozzles. In order to make it possible to effect the precise ink discharge as described above, it is necessary to avoid any contamination of foreign matters which inhibit the flow of the ink in the ink flow passage in the apparatus. Therefore, the contamination of foreign matters is intended to be avoided, for example, as follows. That is, the ink flow passage is assembled and the ink is produced in the clean room, and the ink, which has been subjected to the precise filtration through a membrane filter of 0.2 μm, is used.
In general, a resin or rubber material, which is cheap and easily processible, is used as the material for constructing the ink flow passage of the ink-jet recording apparatus. Usually, such a resin or rubber material contains many additives other than the major component. The additives include, for example, stabilizers such as stannum compounds, fatty acid calcium salts, and phosphorous acid esters to avoid the qualitative deterioration caused by the heat during the molding; fillers such as glass, silica, and metal powders to improve, for example, the heat resistance and the abrasion resistance; ultraviolet-absorbing agents such as 2-hydroxybenzophenone, triazole, and acrylonitrile derivatives to avoid the deterioration of the strength caused by the ultraviolet light; flame retardants such as antimony oxide, barium metaborate, and phosphate esters to improve the flame resistance; plasticizers such as phthalic diesters, dioctyl phthalate, and butanol diesters to adjust the processibility; antioxidants to avoid the deterioration of the strength caused by the air oxidation; antistatic agents such as fatty acid glycerides including, for example, stearic monoglyceride and palmitic monoglyceride to avoid the accumulation of static electricity; coloring agents; and mold releasing agents. Further, any reaction catalyst, which is represented by the chlorine-based catalyst containing carbon tetrachloride, is necessarily used especially for those produced by the ionic polymerization method, such as polyethylene and polypropylene included in the resin or rubber materials. When the chlorine-based catalyst is used as described above, it is necessary to add a neutralizing agent in order that the mold is not corroded during the molding. Fatty acid derivatives such as calcium stearate are used most generally as the neutralizing agent.
Those having the property to be eluted into water are included in the additives as described above. Therefore, even when the ink flow passage is assembled and the ink is produced in the clean room, the clean state can be maintained only at the initial stage at which the ink flow passage is filled with the ink. If the temperature change and/or the time-dependent change occurs in the state in which the ink flow passage is filled with the ink, then the additive is eluted from the resin or rubber material which is used for the ink flow passage, the reaction or the like is caused together with the component contained in the ink, and any insoluble matter is produced in some cases. When such an insoluble matter is produced, a problem arises such that the nozzles are clogged up, the highly accurate ink discharge is not achieved, and the image quality is consequently lowered.
As a technique to solve the problem as described above, Japanese Patent No. 2658034 discloses an ink container in which the content of fatty acid or fatty acid derivative is not more than 100 ppm. However, when the content of fatty acid or fatty acid derivative in the material for the ink container is not more than 100 ppm, the margin for selecting the material is extremely narrowed, which is not practical. Further, according to an experiment performed by the inventors, the discharge failure, which was considered to be caused by the elution of fatty acid or fatty acid derivative, occurred in some cases, although the material, in which the content of fatty acid or fatty acid derivative was about 50 ppm, was used.